Methods to measure energy expenditure (EE) have been understudied in the special needs (SN) population and even less in children who rely on wheelchairs as their primary means of ambulation. This creates a barrier to adequate treatment or prevention of obesity in this high- risk (HR) population. This study, based on the Individual and Family Self-Management Theory (IFSMT) [1] will provide information integral to understanding a crucial construct of weight management in the SN population by evaluating various methods of measuring EE in children with spina bifida (SB), a physical disability, and children with Down syndrome (DS), an intellectual disability. The objectives of the proposed feasibility study are to: 1) determine feasibility of implementing the protocol's subjective and objective measures; 2) determine best placement of accelerometers (waist vs. wrist) based on convenience, feasibility of wearing, and accuracy as compared to the criterion of Doubly Labeled Water (DLW) 3) determine the likelihood of obtaining two different measures of DLW (saliva and urine) and assess the variation between each method; and, 4) identify willingness of parents and children over 13 years of age to complete journaling of physical activity (PA) as well as assess accuracy of journaling as compared to criterion of DLW. Our goal is to recruit 27 children between 4-18 years of age stratified by age, disability and mobility status (wheelchair use). We will obtain the child's height, weight, baseline urine and saliva sample for DLW, resting metabolic cart, general assessment tool. Children will wear a waist and wrist accelerometer for two weeks, obtain urine and saliva samples on day 2, day 7 and day 14, and having the parent and children over 13 years of age complete a timed activity journal for two weekdays and one weekend day of each week that the accelerometers are worn (total of four weekdays and two weekend days). Data analysis will include use of descriptive and correlational tests between waist and wrist worn accelerometers, saliva and urine DLW samples, parental and older child perceptions of total EE and DLW. This feasibility study will lay the groundwork for a trajectory of research that will include a larger study on diet, physical activity and self-management of these chronic conditions.